Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $142.80   13.362%   $161.8809   $161.88   $161.90   $161.90  
  Purchase #2 $199.25   10.369%   $219.9102   $219.91   $219.90   $219.90  
  Purchase #3 $50.34   13.656%   $57.2144   $57.21   $57.20   $57.20  
  Purchase #4 $175.34   5.380%   $184.7733   $184.77   $184.75   $184.80  
  Purchase #5 $144.80   5.709%   $153.0666   $153.07   $153.05   $153.10  
  Purchase #6 $114.42   9.724%   $125.5462   $125.55   $125.55   $125.50  
  Purchase #7 $156.72   3.746%   $162.5907   $162.59   $162.60   $162.60  
  7 purchase totals = $983.67       $1,064.9823   $1,064.98   $1,064.95   $1,065.00